The proposed project will prepare a purified rabbit sperm immobilizing autoantigen from rabbit sperm membranes. Rabbit sperm membranes are prepared by cell homogenization and centrifugation. The membrane proteins are then extracted and separated by ion-exchange chromatography and electrophoresis. Specific autoantigens are identified by their ability to block the sperm immobilizing activity of autoantisera raised in male rabbits by injection of whole ejaculate semen. Specific antibodies will be made in male rabbits to the purified autoantigen. This antisera will be tested for antifertility effects by artificially inseminating female rabbits with antisera treated sperm. These studies should provide a defined macromolecular, sperm-specific, membrane component with which autoimmunity to sperm and its effect on fertility can be explored.